In the processing of circuit boards and cards, the relative thickness required for high volume manufacture employing various commercially available equipment has been a major limiting factor.
For instance, the thickness of the core for circuit boards and cards for various high volume processing has been in the order of about 12 mils or greater.
The cores contain a signal pattern on one side and a blank uncircuitized metallic layer on the other side which can later be made into the external composite surface.
One of the inefficient aspects of the current process employed is that both sides or major surfaces of the core must be processed through all of the photoprocessing and finishing operations, even though such is only required on the signal pattern side.
For instance, the metal, such as the copper on the side which is to function as the blank uncircuitized layer during the photoprocessing, will be entirely covered by a photosensitive material which will remain as such during the photoprocessing, and then be removed in its entirety. As apparent, this is highly wasteful of photoresist material.